Another feature/optimization request (also: macro proposal)

[janderson]

downs wrote:
> Okay, this is more of a compiler than language feature request.
> 
> While writing the OpenGL API for dglut, I found myself repeatedly using the following idiom:
> 
>> void glDoStuff(GLenum foo, int bar, void delegate()[] dgs...) {
>>   auto oldState=glGetStateFooBar(foo);
>>   scope(exit) glStateFooBar(foo, oldState);
>>   glStateFooBar(foo, bar);
>>   
>>   foreach (dg; dgs) dg();
>> }
>>
> 
> Seeing as this, worst-case, comes down to two function call layers, just to do some easier OpenGL stuff, I decided to test how this common situation gets inlined.
> 
> For this, I dumped EBP during several parts of the code.
> 
>> import std.stdio;
>> void test(void delegate()[] dgs...) {
>>         writefln("test: ", getESP());
>>         foreach (dg; dgs) dg();
>> }
>>
>> void *getESP() {
>>         void *res;
>>         asm { mov res, EBP; }
>>         return res;
>> }
>>
>> void main() {
>>         writefln("main: ", getESP());
>>         test({ writefln("dg: ", getESP()); }); 
>> }
>>
> 
> The result: DMD doesn't inline at all. GDC inlines test, but not the delegate.
> 
> Because this might cause significant slowdowns, I'd like to request that the language spec guarantee the following:
> 
> that in a case such as,
> 
>> auto foo={}; foo();
>> // or
>> auto bar=[{}];
>> foreach (b; bar) b(); // foreach can get unrolled at compile-time because the array is static
>>
> 
> foo (and b) always get inlined.
> 
> Note that I propose no kind of complex value tracking, just this one, simple case.
> 
> The effect of this will be to place user-defined control structures taking delegate parameters on the same level as built-in statements.
> 

I think that would be best however I think it should be done with 
templates (I'm not sure if its already possible?):

ie
void glDoStuff(void delegate()[] dgs)(GLenum foo, int bar)
{
    auto oldState=glGetStateFooBar(foo);
    scope(exit) glStateFooBar(foo, oldState);
    glStateFooBar(foo, bar);

    foreach (dg; dgs) dg();
}

 >
[snip]
 >

-Joel